I do have experience messing with the .cfg files for different aircraft. Nothing too complicated so far but enough to know my way around the .cfg file.
Excellent! That makes this much easier. Okay, I'm gonna assume that you know how to edit position numbers for things like the weight and the contact points. If this is the case, simply copy the [smokesystem] section of the Extra 300 config to the one you wish to add smoke to.
Enter FS and notice where the smoke shows up on the aircraft. If it isn't right, just exit and edit the numbers a little. Unfortunately, FS doesn't recognize the longitudinal reference. So that has to be edited in the smoke config itself. For that, I'll have to do another post.
I'll be back in a little bit . . .